435 offset yagi phasing
Hi
I have had good success with just one yagi of an offset crossed array I am building.
http://wa5vjb.com/yagi-pdf/cheapyagi.pdf
I will add the other elements shortly.
I am not ready to tackle the phasing part.
I hope I have this right.
1. The yagi's are offset, by 90 degrees so that is the offset already. 2. Both yagis's should then have the same length of coax coming from each one. 3. Both yagi's will require a 1/4 wavelength of 75 ohm coax for each feed. 4. Remebering that the velocity factor is 2/3 in coax cable, or the speed of light 200 instead of 300. 5. Both 75 ohm feeds then join at a tee, the result of the 50 ohm antenna and 70 ohm feed giving around 120 ohm 6. By tee'ing the two together, this should present around 50 ohm, required for the main feedline.
Does that sound right ?
( 200/435 MHz ) /4 = 11.49 cm for each feed to the tee junction of 75 ohm cable.
---------------------------------------------------------------------------- Andrew Rich VK4TEC
Andrew,
don't spend your time... your questions are already answered on the following pages:
http://sv1bsx.50webs.com/antenna-pol/polarization.html
and also here:
http://hjem.get2net.dk/ole_nykjaer/oz2oe/xyagi/build_yagi.html
Happy New Year
73 de Mak, SV1BSX
----- Original Message ----- From: "Andrew Rich" [email protected] To: "Amsat-Bb@Amsat. Org" [email protected] Sent: Friday, December 28, 2007 13:25 Subject: [amsat-bb] 435 offset yagi phasing
Hi
I have had good success with just one yagi of an offset crossed array I am building.
http://wa5vjb.com/yagi-pdf/cheapyagi.pdf
I will add the other elements shortly.
I am not ready to tackle the phasing part.
I hope I have this right.
- The yagi's are offset, by 90 degrees so that is the offset already.
- Both yagis's should then have the same length of coax coming from each
one. 3. Both yagi's will require a 1/4 wavelength of 75 ohm coax for each feed. 4. Remebering that the velocity factor is 2/3 in coax cable, or the speed of light 200 instead of 300. 5. Both 75 ohm feeds then join at a tee, the result of the 50 ohm antenna and 70 ohm feed giving around 120 ohm 6. By tee'ing the two together, this should present around 50 ohm, required for the main feedline.
Does that sound right ?
( 200/435 MHz ) /4 = 11.49 cm for each feed to the tee junction of 75 ohm cable.
Andrew Rich VK4TEC _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
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I found this page listed below quite interesting. but when it came to offest phasing. I'm lost a little.
Because, of this statement
On the picture above, the centre conductor of the Coaxial-cable is connected to the left part of the Horizontal dipole (as shown the "+"). Thus, the polarity is RHCP (CW).
What happens if you are using a matching system where the dipole is not split? like the awesome matching system used in M squared antennas?
The center conductor is actually going to both sides of the driven element/
Now what?
Joe WB9SBD
SV1BSX wrote:
Andrew,
don't spend your time... your questions are already answered on the following pages:
http://sv1bsx.50webs.com/antenna-pol/polarization.html
and also here:
http://hjem.get2net.dk/ole_nykjaer/oz2oe/xyagi/build_yagi.html
Happy New Year
73 de Mak, SV1BSX
----- Original Message ----- From: "Andrew Rich" [email protected] To: "Amsat-Bb@Amsat. Org" [email protected] Sent: Friday, December 28, 2007 13:25 Subject: [amsat-bb] 435 offset yagi phasing
Hi
I have had good success with just one yagi of an offset crossed array I am building.
http://wa5vjb.com/yagi-pdf/cheapyagi.pdf
I will add the other elements shortly.
I am not ready to tackle the phasing part.
I hope I have this right.
- The yagi's are offset, by 90 degrees so that is the offset already.
- Both yagis's should then have the same length of coax coming from each
one. 3. Both yagi's will require a 1/4 wavelength of 75 ohm coax for each feed. 4. Remebering that the velocity factor is 2/3 in coax cable, or the speed of light 200 instead of 300. 5. Both 75 ohm feeds then join at a tee, the result of the 50 ohm antenna and 70 ohm feed giving around 120 ohm 6. By tee'ing the two together, this should present around 50 ohm, required for the main feedline.
Does that sound right ?
( 200/435 MHz ) /4 = 11.49 cm for each feed to the tee junction of 75 ohm cable.
Andrew Rich VK4TEC _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
avast! Antivirus: Inbound message clean. Virus Database (VPS): 071226-0, 12/26/2007 Tested on: 12/28/2007 14:32:45 avast! - copyright (c) 1988-2007 ALWIL Software. http://www.avast.com
avast! Antivirus: Outbound message clean. Virus Database (VPS): 071226-0, 12/26/2007 Tested on: 12/28/2007 18:05:31 avast! - copyright (c) 1988-2007 ALWIL Software. http://www.avast.com
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Hi Andrew
I am not ready to tackle the phasing part.
Take a look at:
http://www.g6lvb.com/AO-40%2070cm%20uplink%20antenna.htm
Cheers, Howard G6LVB
Ok I have to ask the question.
With offset yagis, those antennae that introduce circular polarisation by means of offsetting the second yagi 90 degress, why would you cut your coax to a 1/4 wave length ?
You already have 90 degrees from the displacement of the yagis.
It should not matter what length the 75 ohm coax is ?
Would it not ?
---------------------------------------------------------------------------- Andrew Rich VK4TEC
The 1/4 wave sections transform the 50 ohm antenna impedances to 100 ohms at the end of the 75 ohm matching section. If you then use a tee to parallel the two antennas, the impedance follows the same rules as paralleled resistances, which means you have a 50 ohm system at the tee.
You can do it another way, too - just tee the 50 ohm lines and off the tee run a 1/4 wave section of 37 ohm cable, made with two runs of 75 ohm coax in parallel. This transforms the 25 ohm impedance at the tee back up to 50 ohms at the end of the matching section.
I don't know which is superior - you have your options, though.
Andrew Rich wrote:
Ok I have to ask the question.
With offset yagis, those antennae that introduce circular polarisation by means of offsetting the second yagi 90 degress, why would you cut your coax to a 1/4 wave length ?
You already have 90 degrees from the displacement of the yagis.
It should not matter what length the 75 ohm coax is ?
Would it not ?
Andrew Rich VK4TEC
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
I know that, but why does it have to be 1/4 wave ?
I have made it so now, and added a pre-amp as well
Now we sit and wait for a satellite
---------------------------------------------------------------------------- Andrew Rich VK4TEC [email protected] mailto:[email protected] http://www.tech-software.net
-----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of jonny 290 Sent: Saturday, 29 December 2007 11:29 AM To: [email protected] Subject: [SPAM] [amsat-bb] Re: 435 offset yagi phasing Importance: Low
The 1/4 wave sections transform the 50 ohm antenna impedances to 100 ohms at the end of the 75 ohm matching section. If you then use a tee to parallel the two antennas, the impedance follows the same rules as paralleled resistances, which means you have a 50 ohm system at the tee.
You can do it another way, too - just tee the 50 ohm lines and off the tee run a 1/4 wave section of 37 ohm cable, made with two runs of 75 ohm coax in parallel. This transforms the 25 ohm impedance at the tee back up to 50 ohms at the end of the matching section.
I don't know which is superior - you have your options, though.
Andrew Rich wrote:
Ok I have to ask the question.
With offset yagis, those antennae that introduce circular polarisation by means of offsetting the second yagi 90 degress, why would you cut your coax to a 1/4 wave length ?
You already have 90 degrees from the displacement of the yagis.
It should not matter what length the 75 ohm coax is ?
Would it not ?
--
Andrew Rich VK4TEC
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
_______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Andrew, Yes that is correct with one exception that a 50 ohm, 1/2 wave section needs to be inserted for the opposite rotation in one antenna. This is switched in and out with a coax switch or relay. The 1/4 wave sections do the matching and both offer the same delay so there is no phase difference to the antennas. As the antennas are 1/4 wave offset one leads by 90 degrees. adding a 180 degree delay will cause that antenna to lag by 90 degrees and hence the opposite rotation.
Good luck with the project. Learning by doing is the best way!
Art, KC6UQH ----- Original Message ----- From: "Andrew Rich" [email protected] To: "Amsat-Bb@Amsat. Org" [email protected] Sent: Friday, December 28, 2007 3:25 AM Subject: [amsat-bb] 435 offset yagi phasing
Hi
I have had good success with just one yagi of an offset crossed array I am building.
http://wa5vjb.com/yagi-pdf/cheapyagi.pdf
I will add the other elements shortly.
I am not ready to tackle the phasing part.
I hope I have this right.
- The yagi's are offset, by 90 degrees so that is the offset already.
- Both yagis's should then have the same length of coax coming from each
one. 3. Both yagi's will require a 1/4 wavelength of 75 ohm coax for each feed. 4. Remebering that the velocity factor is 2/3 in coax cable, or the speed of light 200 instead of 300. 5. Both 75 ohm feeds then join at a tee, the result of the 50 ohm antenna and 70 ohm feed giving around 120 ohm 6. By tee'ing the two together, this should present around 50 ohm, required for the main feedline.
Does that sound right ?
( 200/435 MHz ) /4 = 11.49 cm for each feed to the tee junction of 75 ohm cable.
Andrew Rich VK4TEC _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
http://www.tech-software.net/antennae/index.html
Updated photo gallery
---------------------------------------------------------------------------- Andrew Rich VK4TEC
G'day Andrew, Photos look great but I would suggest to get the most from your helix you should use a larger reflector, it's generally 1 wavelength diam. is OK. This does create a much greater wind loading, especially on the lower Frq's , probably one reason why they haven't gained more popularity. If matched properly you should be able to get a 1:1 SWR I have just upgraded my 2m helix (no photos available yet) The 10 turn helix was previously made of 3 mm hard drawn copper wire. I have just replaced the helix with 15 x 2 mm aluminum strap. This has improved the gain considerably, I won't quote figures because I don't believe i have test gear to accurately measure antenna gain.
See :- http://www.electric-web.org/tracking_antenna.htm Also :- http://www.electric-web.org/2m_helix_antenna.htm
Regards Tony. VK5ZAI
J.A.(Tony)Hutchison P.O.Box 470 Kingston SE South Australia 5275
National ARISS Co-ordinator and Satellite ground Station.
Web Site :- http://www.electric-web.org
Andrew Rich wrote:
http://www.tech-software.net/antennae/index.html
Updated photo gallery
Andrew Rich VK4TEC
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
----- Original Message ----- From: "Andrew Rich" [email protected] To: "jonny 290" [email protected]; [email protected] Sent: Saturday, December 29, 2007 3:25 AM Subject: [amsat-bb] Re: [SPAM] Re: 435 offset yagi phasing
I know that, but why does it have to be 1/4 wave ?
Hi Andrew, VK4TEC
Because only a 1/4 electrical wave or any odd numbar of 1/4 electrical wave of 75 ohm transmission line make the impedance transformation from the 50 ohm impedance of the antenna to 112.5 ohm as follows:
112.5 = 75^2 / 50
I have made it so now, and added a pre-amp as well
Now we sit and wait for a satellite
--
Andrew Rich VK4TEC
73" de
i8CVS Domenico
-----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of jonny 290 Sent: Saturday, 29 December 2007 11:29 AM To: [email protected] Subject: [SPAM] [amsat-bb] Re: 435 offset yagi phasing Importance: Low
The 1/4 wave sections transform the 50 ohm antenna impedances to 100 ohms at the end of the 75 ohm matching section. If you then use a tee to parallel the two antennas, the impedance follows the same rules as paralleled resistances, which means you have a 50 ohm system at the tee.
You can do it another way, too - just tee the 50 ohm lines and off the tee run a 1/4 wave section of 37 ohm cable, made with two runs of 75 ohm coax in parallel. This transforms the 25 ohm impedance at the tee back up to 50 ohms at the end of the matching section.
I don't know which is superior - you have your options, though.
Andrew Rich wrote:
Ok I have to ask the question.
With offset yagis, those antennae that introduce circular polarisation
by
means of offsetting the second yagi 90 degress, why would you cut your coax to a 1/4 wave length ?
You already have 90 degrees from the displacement of the yagis.
It should not matter what length the 75 ohm coax is ?
Would it not ?
--
Andrew Rich VK4TEC
participants (8)
-
Andrew Rich -
Howard Long -
i8cvs -
Joe -
jonny 290 -
kc6uqh -
SV1BSX -
Tony VK5ZAI